Messages

My experience is that there is a big difference between having a convex knife from the start compared to converting a straight knife to a convex one. A convex edge is stronger and more material on than on a straight edge as picture A shows. Picture B shows what happens when you sharpen a straight knife to convex. If you turn a convex edge into a straight edge, you also lose material just like turning a straight edge into a convex edge. It depends on what you start with.
On a convex original knife, the radius of the convex sphere is often smaller than if you turn a straight edge into a convex one because you cannot add material. The radius is drawn green in the image. The only way to reduce the radius is to move the tip so that the blade becomes less high.

Correction:
cbwx34 helped me to understand one thing that i mist. Thanks cbwx34
I made a mistake when I wrote that it is 1,4 degrees convex.
I did not accounting for the change in the actual angle on the curved surface , just the angle change of the jig. There is probably neared 7 degrees in actual change. Sorry

I think it will be difficult to get a nice convex edge with the new jig. It feels a bit "swaying" when you switch between the positions and difficult to move the knife in two directions at the same time and it becomes an, unwanted stop with the edge against the grinding wheel, which I find difficult to handle. As you can see on pic1-2, there is about 1.4 degrees (Slightly convex) difference between the two positions. It can work on a small edge, but on forest knives similar to F1 (https://fallkniven.se/en/home/) a medium convex or high convex is needed.
I think it is easier with a jig as in picture 31-33 which is more accurate for convex knives and where you have greater control at all angles. I will probably not grind convex with kj-45. It will be interesting to hear what you others think when you get the opportunity to test kj-45.

That knife was about 30mm high
2mm is the least you need to be able to clamp, according to Tormek, and it is possible to slide the knife up to 13.5mm in the jig. So you can fasten knives with between 24.5 to 36mm high blades and  have the opportunity to set the projection distance to 139mm. Otherwise you have to specify the projection distance you get in a program.

Works well in my opinion after a week of use. I use 11.7mm as a new measure for jig diameter and it works well. With an ordinary kitchen knife, you are close to 140mm in projection distance. I like it and will use it a lot.
I enclose some measurements for those of you who are curious ..

Good job. I have tested and it fits well with my own measurements. It really makes it easier to find the right distance. Thank you so much for sharing. I intend to copy it and use it in my own program.   

On request, I enclose here an angle program in excel that can be used together with this tool to set the grinding angle of your Tormek. You can also try using an angle cube with it if you want.
Feel free to leave a comment about what you think or if you see something that is wrong.
Calculations and inputs in the program are most the same as in other programs but I have added calculations for an angle cube.
My ambition has been to make a slightly easier program to use than the fantastic Tormekcalc2 that can do so much more.

I think I will take this to our library.s 3D printer and give it a go.

Thanks

Glad you appreciate it and want to try making your own. I use it all the time.

You can also use it the together with TormekCalc2 and an angle cube. Just turn it upside down but be sure that the ruler is long enough to rest on the grinding wheel. Pic16

I have also worked with a way to set the grinding angle with an angle cube and this tool, and have created my own excel file for it. If there is anyone who is interested, just let me know and I can upload it on the forum.

It is not easy to use an angle cube because the value only changes by 0.6 degrees on the angle cube for each full degree you change the grinding angle. Therefore, you need a very precise angle cube. But it can be fun to try.

I'm been working with this problem also and come up with this solution.
I have tried to seek simplicity and not to destroy any existing characteristics. Everything on the jig works as usual.
The principle is to be able to use eccentricity to move the center of the shaft of the jig and thus center the knife holder after different knife thicknesses. Cut of the jig in appropriate place. Insert a 6.0 mm shaft pin that sits 2.0 mm out of the center of the shaft, which allows me to move the center of the jig 0 - 2.0 mm by turning the bracket. This allows me to center knives in the jig up to 3.1 mm out of the center (about 1.1 mm is available right from the start)It gives me the opportunity to center knives that are up to 6.2 mm in thickness. And also knives that are thinner than 2 mm. The process is simple. I put a knife in the jig, place as usual on the T8, measure both sides with the WM-200 and note the angles. Then turn the bracket until I get the same angular value on both sides. (Halves the angular difference) Lock with the locking screw. Insex M4. Maybe grind/lathe a small v-groove in the shaft also so the locking screw also locks axially. There will be a small side movement on the knife and there will be a (theoretical) angular error when tipping up the tip. But I can't see it's a practical problem! The next step is to measure and mark (draw in) positions on the two axes for different knife thicknesses, then you can theoretically center the jig in advance if you know the thickness of the knife where it is clamped. Rework requires some craft work but, on the other hand, costs almost nothing. Cutting, drilling, threading + one 6 mm pin (one M6 bolt goes well) and a locking screw M4 I did not press in the pin but threaded M6 and screwed it in.  I have not noticed that it weakened or in any way became unstable in the jig when grinding.  This is a possible jig solution for knifes with different thicknesses, maybe not for knives that have a tapered blade.

Looks cool! Which printer are you using and are you uploading your files to a place like thingyverse?

Here is the file for 3d -print.

I'm not going to argue with you,  I agree with what you're saying. Thanks for the wise words and interesting tips. I appreciate it.  In my own excel file, I actually round the values to full or half mm.

Simple solutions are usually the most widely used. Smart ide with a rubber band. I agree that it gets a little "nerdy" with precision in several decimal places. But sometimes it's just fun to solve problems. I both grind and hone with the knife stuck in the jig and then it will be interesting to get the right angle also on the honing wheel, usually added 1-2 degrees. My experience is that the sharpness gets better then when I'm honing freehand. I can contribute with a CAD image where I measured how little it differs if you measure at the rubber band in relation to measurement in the center line. 0.145mm

Hi Micha
Thanks. I notice that and its a nice solution but its hard to read under 1mm. i will have a way to use a calliper, but maybe i miss anything?

Is there anyone more than me who had difficulty measuring the correct height of the grinding wheel to the Usb? I had difficulty measuring straight against the grinding wheel and wanted a 90 degree surface to measure against instead. I have searched for suggestions and tips but not found anything where you measure with calipers etc.
So it became a prototype like these. I've been thinking about 3D printing one or making in metal.
Any other suggestions or tips!

No I not upload any file for this tool. i do belive that the picture explain how to make one if you are interested. And the most importent value is 6mm that I also markt on the picture. You can choose the dimensions as you like on the rest of the tool to fit any ruler, etc.